What do I need to make a custom theme?
And if possible, where can i download these programs?
Much Obliged.

Well the first thing you need to do is learn how to SSH. You can youtube that lol.

Things you need on your phone will be Winterboard, SBSettings, OpenSSH(wifi ssh) and/or afc2add(usb ssh)
-if on windows program you need is WinSCP for wifi, or ifunbox for usb transfers.
-Mac its cyberduck for wifi and i dont know about usb

But after you know how you can download THIS. Its the stock iphone theme. All the files and folders are in the right place, you just have to replace them with what you want.